There is a long felt need for autonomous robotic cleaning and processing devices for dusting, mopping, vacuuming, sweeping, lawn mowing, ice resurfacing, ice melting, and other operations. Although technology exists for complex robots which can, to some extent, “see” and “feel” their surroundings, the complexity, expense and power requirements associated with these types of robotic subsystems render them unsuitable for the consumer marketplace.
The assignee of the subject application has devised a less expensive, battery operated, autonomous cleaning robot which operates in various modes, including random bounce and wall-following modes. In the random bounce mode, the processing circuitry of the robot causes it to move in a straight line until the robot comes into contact with an obstacle; the robot then turns away from the obstacle and heads in a random direction. In the wall-following mode, the robot encounters a wall, follows it for a time, and then returns to the random mode. By using this combination of modes, robotic theory has proven that the floor, including the edges thereof, is adequately covered in an optimal time resulting in a power savings.
Unfortunately, however, presently available sensor subsystems such as sonar sensors for detecting obstacles on or in the floor or for detecting the wall in order to enter the wall-following mode (or to avoid bumping into the wall) are either too complex or too expensive or both. Tactile sensors are inefficient to ensure that walls or other obstacles can be effectively followed at a predetermined distance.
Some existing systems that disclose wall-following modes for autonomous robots are disclosed in International Publication No. WO 02/101477 A2, U.S. patent application Ser. No. 10/453,202 and U.S. Pat. No. 6,809,490, the disclosures of which are herein incorporated by reference in their entireties. In an embodiment of the system disclosed in the U.S. patent and application (and available commercially from iRobot Corporation as the ROOMBA® Robotic Floorvac), analog electronics (i.e., a comparator) are used to determine whether a sensor has detected the wall or not. The system is designed to follow along a wall at a predetermined distance to allow a cleaning mechanism (e.g., a side brush) to clean against a wall. In the ROOMBA® Robotic Floorvac, a mechanical shutter proximate the sensor can be manually adjusted by the user in order to make the robot follow an appropriate distance from the wall. This shutter is used since the sensor can be sensitive to the albedo of the wall. This manually adjusted shutter, while effective, detracts from the autonomous nature of mobile robots; thus, a fully independent wall-following scheme for a mobile robot is needed.